Tesla shares have surged about 300% in the past six months, hitting an all-time high of over $900 on Tuesday. Traders, analysts, and politicians are lining up to warn investors that the run up won't last.

"This is obviously a computer-generated rally, it's not a reflection on the company, or on valuation. It's just a trade," Andrew Left, the activist short seller behind Citron Research, told MarketWatch this week.

"Yes, I'm shorting it ... whoever bought it at these prices has to flush it out, and when it flushes, it's going to flush hard," he added.

"We believe even Elon would short the stock here if he was a fund manager," the equity-research publisher tweeted on Tuesday. "This is no longer about the technology, it has become the new Wall St casino."

Others have warned Tesla's rally will hurt those left holding the stock when the music stops.

"This is an incredibly dangerous place to be buying the stock and I have no doubt it will end in tears for many people," trader and analyst Jani Ziedins wrote in a recent post on his Cracked Market blog.

"Owning a stock that's tripled over the last few months is great, but don't mistake serendipity for skill," he continued. "While the fools are spending all of their time daydreaming about what they will buy when the stock breaks $1,200, smart money is selling their stock to those greedy dreamers."